Interactive whiteboards generally utilize a sensing surface coupled to a computer to detect where a stylus is interacting with the surface. Different technologies, such as infrared scan type whiteboards detect where a pointer or stylus is based on interference with infrared light at the whiteboard surface. Software may be used to triangulate the position of the pointer or stylus. Resistive touch whiteboards utilize a resistive membrane on the surface of the whiteboard to sense where a person is drawing. Electromagnetic based whiteboards utilize an array of wires in the whiteboard that interact with a coil in a passive pen. Other types of whiteboards operate on different principles, including projector based. Such whiteboards can be fairly expensive and dedicated to a single whiteboard purpose.